perf stat: Implement control commands handling

Implement handling of 'enable' and 'disable' control commands coming
from control file descriptor. If poll event splits initiated timeout
interval then the reminder is calculated and still waited in the
following evlist__poll() call.

Committer testing:

The testing instructions came in the cover letter, here I'll extract the
parts that are needed to test this specific patch, so that we don't
introduce bisection regressions by testing only the patch series as a
whole:

<FILL IN THE TEST INSTRUCTIONS>

Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/3cb8a826-145f-81f4-fcb2-fa20045c6957@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-stat.c

@@ -560,9 +560,61 @@ static bool is_target_alive(struct target *_target,
 	return false;
 }
 
-static int dispatch_events(bool forks, int timeout, int interval, int *times, struct timespec *ts)
+static void process_evlist(struct evlist *evlist, unsigned int interval)
+{
+	enum evlist_ctl_cmd cmd = EVLIST_CTL_CMD_UNSUPPORTED;
+
+	if (evlist__ctlfd_process(evlist, &cmd) > 0) {
+		switch (cmd) {
+		case EVLIST_CTL_CMD_ENABLE:
+			pr_info(EVLIST_ENABLED_MSG);
+			if (interval)
+				process_interval();
+			break;
+		case EVLIST_CTL_CMD_DISABLE:
+			if (interval)
+				process_interval();
+			pr_info(EVLIST_DISABLED_MSG);
+			break;
+		case EVLIST_CTL_CMD_ACK:
+		case EVLIST_CTL_CMD_UNSUPPORTED:
+		default:
+			break;
+		}
+	}
+}
+
+static void compute_tts(struct timespec *time_start, struct timespec *time_stop,
+			int *time_to_sleep)
+{
+	int tts = *time_to_sleep;
+	struct timespec time_diff;
+
+	diff_timespec(&time_diff, time_stop, time_start);
+
+	tts -= time_diff.tv_sec * MSEC_PER_SEC +
+	       time_diff.tv_nsec / NSEC_PER_MSEC;
+
+	if (tts < 0)
+		tts = 0;
+
+	*time_to_sleep = tts;
+}
+
+static int dispatch_events(bool forks, int timeout, int interval, int *times)
 {
 	int child_exited = 0, status = 0;
+	int time_to_sleep, sleep_time;
+	struct timespec time_start, time_stop;
+
+	if (interval)
+		sleep_time = interval;
+	else if (timeout)
+		sleep_time = timeout;
+	else
+		sleep_time = 1000;
+
+	time_to_sleep = sleep_time;
 
 	while (!done) {
 		if (forks)
@@ -573,9 +625,16 @@ static int dispatch_events(bool forks, int timeout, int interval, int *times, st
 		if (child_exited)
 			break;
 
-		nanosleep(ts, NULL);
+		clock_gettime(CLOCK_MONOTONIC, &time_start);
-		if (timeout || handle_interval(interval, times))
+		if (!(evlist__poll(evsel_list, time_to_sleep) > 0)) { /* poll timeout or EINTR */
-			break;
+			if (timeout || handle_interval(interval, times))
+				break;
+			time_to_sleep = sleep_time;
+		} else { /* fd revent */
+			process_evlist(evsel_list, interval);
+			clock_gettime(CLOCK_MONOTONIC, &time_stop);
+			compute_tts(&time_start, &time_stop, &time_to_sleep);
+		}
 	}
 
 	return status;
@@ -644,7 +703,6 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
 	char msg[BUFSIZ];
 	unsigned long long t0, t1;
 	struct evsel *counter;
-	struct timespec ts;
 	size_t l;
 	int status = 0;
 	const bool forks = (argc > 0);
@@ -653,17 +711,6 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
 	int i, cpu;
 	bool second_pass = false;
 
-	if (interval) {
-		ts.tv_sec  = interval / USEC_PER_MSEC;
-		ts.tv_nsec = (interval % USEC_PER_MSEC) * NSEC_PER_MSEC;
-	} else if (timeout) {
-		ts.tv_sec  = timeout / USEC_PER_MSEC;
-		ts.tv_nsec = (timeout % USEC_PER_MSEC) * NSEC_PER_MSEC;
-	} else {
-		ts.tv_sec  = 1;
-		ts.tv_nsec = 0;
-	}
-
 	if (forks) {
 		if (perf_evlist__prepare_workload(evsel_list, &target, argv, is_pipe,
 						  workload_exec_failed_signal) < 0) {
@@ -821,7 +868,7 @@ try_again_reset:
 		enable_counters();
 
 		if (interval || timeout)
-			status = dispatch_events(forks, timeout, interval, &times, &ts);
+			status = dispatch_events(forks, timeout, interval, &times);
 		if (child_pid != -1) {
 			if (timeout)
 				kill(child_pid, SIGTERM);
@@ -838,7 +885,7 @@ try_again_reset:
 			psignal(WTERMSIG(status), argv[0]);
 	} else {
 		enable_counters();
-		status = dispatch_events(forks, timeout, interval, &times, &ts);
+		status = dispatch_events(forks, timeout, interval, &times);
 	}
 
 	disable_counters();